Disability in later life is a serious problem for women, threatens their independence, and results in significant health care needs and expenditures. Women live longer than men and suffer disproportionately from disability and its consequences. An understanding of the processes leading to disability is essential in order to develop strategies to prevent or delay disability. Sarcopenia, defined as loss of muscle mass and muscle strength, plays a central role in disability and contributes to mobility disability, difficulty with activities of daily living, and increased risk of falls and hospitalizations. Recently, several lines of evidence have emerged to suggest that oxidative stress is involved in the pathogenesis of sarcopenia. We hypothesize that oxidative stress is an independent predictor of sarcopenia, impaired physical performance, disability, and mortality in older women. We also hypothesize that women who maintain a high level of antioxidants and low level of oxidative damage over time are at lower risk of sarcopenia, impaired physical performance, disability, and mortality. Our specific aims are: (1) to characterize oxidative stress by measuring antioxidant nutrients and oxidative damage to DMA, protein, and lipids over time in two related population-based cohorts of older women, (2) to examine the relationship between changes in oxidative stress and sarcopenia (loss of muscle mass and muscle strength) over time, and (3) to examine the relationship between oxidative stress and more distal, related outcomes of sarcopenia (impaired physical performance, disability, and mortality). To address these aims, we plan to conduct a prospective study of oxidative stress in two related population-based longitudinal cohorts of older women, the Women's Health and Aging Studies (WHAS) I and II. WHAS I and II are two complementary studies of the role of chronic diseases on disability in the one-third most, and two- thirds least disabled older women living in the community, respectively. We will measure carotenoids, tocopherols, and selenium, and oxidative damage to DNA, protein, and lipids from samples in an existing repository. These new data will build on the long-term goal of WHAS to understand the pathogenesis of disability in older women, an issue of major public health importance. This study should provide greater insight into the major paradigm of oxidative stress and aging and help to develop strategies for the identification of high-risk individuals and the prevention of sarcopenia and disability in older women.